Build a Tower of Liatris
Liatris buds open from the tip down, so their bright lilac color appears to stream down the length of their stems to give this dramatic design an atmospheric effect. Make several arrangements, of the same or different sizes, for variety.
From: DK Books - Flower Arranging
If you can't find liatris, use monkshood or gentian.
tall black cube vase (16 1/2 inches high)
cellophane or plastic bags
1 block floral foam
How to Arrange
Pack some scrunched-up cellophane or plastic bags inside the vase until it is about two-thirds full.
Trim a soaked block of floral foam so that it fits snugly inside the vase just below the rim.
Trim the liatris stems so they are all about 20–22 inches, or a little longer than the height of the container. Press the stems firmly into the foam in straight lines, placing them as close to each other as possible and working from the front of the vase to the back. Twist the stems slightly as you press them in so that they stand as straight as possible and don't flare out to the sides.
Liatris require very little aftercare once they have been arranged, so just mist the flowers occasionally. The arrangement should last for seven to 10 days if you keep the foam wet.
Lines of Liatris
The liatris should be placed firmly and methodically in straight lines to maintain the strict geometry of this proportion-focused design. Try to get the placement right the first time and not pull them out to rearrange them, or the floral foam will start to disintegrate.